2024-09

Structural Chemistry (Issue : 5) (Volume : 35)

The [3 + 2] cycloaddition (32CA) reactions involving 6-butoxy-5,6-dihydro-4H-1,2-oxazine 2-oxide and dimethyl maleate are examined in this study. Molecular electron density theory (MEDT) is applied at the M06-2X/6-311G(d,p) level, coupled with the D3 dispersion correction. The nitronate 1 species are identified as zwitterionic entities through an analysis of the electron localization function (ELF). This 32CA reaction follows an asynchronous one-step mechanism. Conceptual DFT indices are utilized to classify dimethyl maleate as the electrophilic component and the nitronate as the nucleophilic counterpart. The [3 + 2] cycloaddition processes are predominantly governed by kinetic control, as indicated by activation free energies of − 23.6 and − 11.4 kcal.mol−1 for the exo and endo pathways, respectively, aligning with experimental findings. Despite the nucleophilic and electrophilic character of the reagents, the global electron density transfer at the TSs indicates rather polar 32CA reactions. The formation of a pseudoradical center initiates at carbon atoms C3 and C4. A subsequent docking analysis is conducted on cycloadducts 3 and 4 in relation to the main protease of SARS-CoV-2 (6LU7), alongside the co-crystal ligand. The results of this analysis reveal that cycloadducts 3 exhibit higher binding energy, while cycloadducts 4 display lower binding energy compared to the co-crystal ligand. The results confirm that the presence of isoxazolidine ring increases the affinity of the product 3.

2024-09

Journal of Molecular Structure (Issue : 3) (Volume : 1321)

A novel category of hybrids, termed (Z)-6-methyl-3-(1-((1-(prop‑2-yn-1-yl)-1H-indazol-6-yl)amino)ethylidene)-2H-pyran-2,4(3H)‑dione, was synthesized by reductive coupling of N-alkyl-6-nitroindazoles and 2-pyrone using indium or stannous chloride in tetrahydrofuran (THF) with acetic acid. This process yielded (Z)-2H-pyran-2,4(3H)-diones in satisfactory yields. Each synthesized molecule underwent comprehensive characterization through NMR analysis and X-ray diffraction. Additionally, our investigation incorporates quantum chemical modeling via density functional theory (DFT) at the B3LYP/6–311G(d,p) level, along with molecular docking analysis. An analysis of the Hirshfeld molecular surface was undertaken to characterize the type of intermolecular connections. The percentage contributions, shown in the footprint plot, indicate that H…H interactions (33.0 %) are particularly significant in the constitution of the crystal. The favorable pharmacological properties of compounds 5a and 6a, such as good bioavailability, ability to penetrate the blood-brain barrier, and adherence to the Lipinski rule, make them excellent candidates for therapeutic development.

2024-08

EXCLI Journal (Volume : 23)

The coexistence within a subcellular complex of inter-cellular proteins Ro60, responsible for preserving ncRNA quality, and Ro52, involved in intracellular proteolysis, has been a subject of ongoing debate. Employing molecular docking in tandem with experimental methods like Quartz Crystal Microbalance with Dissipation (QCM-D), Proximity Ligation Assay (PLA), and Indirect Immunofluorescence (IIF), we reveal the presence of Ro60 associating with Ro52 within the cytoplasm. This result unveils the formation of a weak transient complex with a Ka ≈ (3.7 ± 0.3) x 106 M-1, where the toroid-shaped Ro60 structure interacts with the Ro52's Fc receptor, aligning horizontally within the PRY-SPRY domains of the Ro52's homodimer. The stability of this complex relies on the interaction between Ro52 chain A and specific Ro60 residues, such as K133, W177, or L185, vital in the Ro60-YRNA bond. These findings bridge the role of Ro60 in YRNA management with Ro52's function in intracellular proteolysis, emphasizing the potential impact of transient complexes on cellular pathways.

2024-08

Heliyon (Issue : 15) (Volume : 10)

In this study, we screened novel dipeptidyl peptidase IV (DPP4) inhibitors from the ConMedNP library consisting of 3507 molecules. Interestingly, molecular docking, ADMET, and the anti-diabetic activity predictions suggest that three molecules, namely OTH_UD_XX06_1, GB19, and BMC_000104, have a high binding affinity toward DPP4. The molecular dynamics (MD) simulation results suggest that these hit molecules have a stable binding pose and occupy the binding pockets throughout the 200 ns simulation. The presence of intermolecular H-bonding between the ligands and DPP4 was observed throughout the simulation period. Thus, docking and MD results, predicted that the three compounds were the most potent DPP4 inhibitors that could putatively bind to the DPP4 active site via both conventional H-bonding and hydrophobic interactions. These results could aid the discovery of new drugs to treat type 2 diabetes.

2024-06

Chemical Monthly (Issue : 6) (Volume : 155)

The study explores the application of molecular electron density theory, focusing on the [2 + 3] cycloaddition mechanisms between nitrile-imine and chalcone or thiochalcone. Density Functional Theory (DFT) calculations employing the B3LYP/6–311(d,p) methodology are utilized to determine activation and reaction energies, as well as reactivity indices. Through investigation of conceptual DFT indices, nitrile-imine is identified as a nucleophile, while chalcone and thiochalcone act as electrophiles in the reaction. The reactions exhibit both chemo- and regiospecifics, as confirmed by Parr functions, Electron Localization Function (ELF) survey, and energetic analysis, consistent with experimental results. ELF analysis suggests a two-phase mechanism for these [2 + 3] cycloadditions. Furthermore, docking studies on the resultant products reveal enhanced interaction energies with proteins due to the presence of oxygen and sulfur atoms, in their interaction with the crystal structure of COVID-19 main protease (PDB ID: 6LU7) and paves a ways for manufacturing innovation.

2024-05

Computational and Theoretical Chemistry (Issue : 5) (Volume : 1237)

The [3 + 2] cycloaddition reactions of N-methyl-C-(2-furyl) nitrone (a) with a series of acetylene derivatives (4b), (5b), and (6b) have been studied at the B3LYP-D3/6-31G(d) computational level within the framework of Molecular Electron Density Theory. Topological analysis allows classifying the nitrone (a) as a zwitterionic (zw-) three-atom component (TAC) associated with high energy barrier. These 32CA reactions follow a one-step mechanism under kinetic control with highly asynchronous bond formation. Bonding Evolution Theory (BET) analysis indicates that no new covalent Csingle bondO and Csingle bondC bonds form at the transition states (TSs). Interestingly, the global electron density transfer (GEDT) between 0.08 and 0.18 e predicts low polar character of forward electron density transfer (FEDF) type with the electronic flux from the nitrone (a) to the acetylene derivatives. Electron localization function (ELF) and atom-in-molecules (AIM) topological analysis of the electron density at the TS structures characterize the non-concerted nature of these one-step zw-type 32CA reactions.

2024-05

Journal of Molecular Structure (Volume : 1312)

This research investigates the inhibitory performance of BM-02, a synthesized pyrazole derivative (R)-5-(4-methoxyphenyl)-1,3-diphenyl-4,5-dihydro-1H-pyrazole, against the corrosion of mild steel in a 1 M hydrochloric acid solution. A comprehensive array of experimental techniques, including weight loss analysis, potentiodynamic polarization, electrochemical impedance spectroscopy, and scanning electron microscopy, were employed to assess the inhibitory effectiveness. BM-02 is identified as a mixed inhibitor, showcasing a remarkable efficiency of 91.5 % at a concentration of 10−3 mol/l. The adsorption behavior of the BM-02 molecule was investigated, revealing a physical adsorption model in accordance with the Langmuir isotherm. Furthermore, ATR-IR, 1H NMR, and 13C NMR spectra were acquired, complemented by density functional theory (DFT) calculations and molecular dynamics (MD) simulations to gain deeper insights into the molecular interactions and corrosion inhibition mechanism.

2024-05

Computational and Theoretical Chemistry (Volume : 1237)

The reactivity, regiochemistry and substituent effects observed in the [3 + 2] cycloaddition (32CA) reactions of diphenyldiazomethane (PDM) with thiobenzophenone and a series of cycloaliphatic thioketones (TKs) have been studied within the molecular electron density theory at the ωB97XD/6-311G(d,p) computational level. The cycloaliphatic TK series shows remarkable substituent effects, changing from a non-polar 32CA reaction to a highly polar one, with the electron density flowing from PDM to the corresponding TK in a reaction classified as a forward electron density flux (FEDF). These 32CA reactions follow a one-step mechanism through earlier asynchronous transition state structures in which the formation of the two new single bonds has not yet begun, and the energetically predicted regiochemistry towards the generation of 1,3,4-thiadiazole is in complete agreement with the experimental outcome.

2024-02

Journal of Molecular Structure (Issue : 5) (Volume : 1305)

Allohimachalol, a vital element in Atlas cedar wood essential oil, is obtained through steam distillation, shaping the oil's distinctive aroma. Its prominence enhances the unique olfactory character of cedar oil, making it valuable in perfumery and aromatherapy. To enhance its reactivity, we conducted experimental and theoretical studies on the epoxidation reaction of Allohimachalol with meta-chloroperbenzoic acid (m-CPBA). This reaction led to the formation of a new product, referred to as product 3, through a simultaneous rearrangement process. The compound structures were identified using spectroscopic techniques, including 1H and 13C NMR, along with X-ray diffraction. Furthermore, the electronic structures of the synthesized compounds were investigated through theoretical calculations using density functional theory (DFT) at the B3LYP/6-311G(d,p) level. The analysis of energy profiles related to different reaction pathways produced results in line with the experimental observations, confirming the alignment of the allohimachalol epoxidation reaction with theoretical predictions. Additionally, a docking analysis was performed on the investigated compounds within the primary protease of SARS-CoV-2 (6LU7) and HIV, indicating that compound 3 holds promise as a potential antiviral drug for human health.

2024-01

Structural Chemistry (Issue : 6) (Volume : 34)

The intramolecular [3 + 2] cycloaddition (IM32CA) reactions of azides and diazoalkanes leading to fused tricyclic 1,2,3-triazolines and 1-pyrazolines have been studied at the MPWB1K/6-311G(d,p) computational level within the molecular electron density theory (MEDT). The IM32CA reactions of azides are classified as zw- type following non-concerted one-step mechanism with earlier N1-C5 bond formation implied from the bonding evolution theory (BET) study with the Gibbs free activation energies between 26.3–30.0 kcal mol−1 at 298 K in benzene while that of the diazoalkanes are classified as pmr- type with the earlier C3-C5 bond formation and Gibbs free activation energies between 24.7–29.1 kcal mol−1 at 298 K in n-pentane. The influence of substituent effects on these IM32CA reactions is studied. Azide reactions with minimal global electron density transfer (GEDT) are classified as the null electron density flux (NEDF) while that of the diazoalkanes are classified as forward electron density flux (FEDF). QTAIM analysis and ELF study allow revealing the non-covalent interactions at the TSs.

2023-11

Theoretical Chemistry Accounts (Issue : 12) (Volume : 142)

The [3+2] cycloaddition (32CA) reaction between cyclic azomethine ylide (generated from N-phenacylquinolinium bromide) and N-arylmaleimide, leading to pyrrolo[1,2-a]quinolone, has been investigated using the Molecular Electron Density Theory at the B3LYP/6-311++G(d,p) computational level with D3 correction. This study focuses on the zwitter-ionic type 32CA reaction, highlighting its polar character with the electronic flux from the azomethine ylide to the alkene. The reaction proceeds with complete endo-stereoselectivity, and the activation parameters show minimal variations in different solvents, consistent with experimental observations. The activation energy is associated with the depopulation of the N2–C1 and C4–C5 bonding regions, formation of non-bonding electron density at N2 nitrogen and creation of pseudoradical centers at C3, C4 and C5. These findings suggest that the formation of new covalent bonds does not occur at the transition states, in line with the presence of non-covalent interactions at the interatomic bonding regions, as revealed by the topological analysis of the Quantum Theory of Atoms-in-Molecules.

2023-11

Computational and Theoretical Chemistry (Volume : 1230)

The [3 + 2] cycloaddition (32CA) reactions of C-(4-methoxyphenyl)-N-phenyl nitrile imine (NI) with a series of ethylene derivatives of increased electrophilic character have been studied within the framework of Molecular Electron Density Theory (MEDT). These 32CA reactions are kinetically controlled with activation Gibbs free energies between 14.8 and 24.0 kcal mol−1, and with the preferred regioselectivity involving the nucleophilic attack of the carbenoid carbon of NI on the non-substituted carbon of the electrophilic ethylenes in agreement with the experimental outcomes. The presence of electron-withdrawing substituents in the ethylene makes the 32CA reaction of forward electron density flux (FEDF) more quickly, relative to that with nucleophilic propene, showing the highest activation parameters and non-polar character. Electron localization function (ELF) and atom-in-molecules (AIM) topological analysis of the electron density at the transition state structures characterize the non-concerted nature of these one-step cb-type 32CA reactions.

2023-08

Computational and Theoretical Chemistry (Volume : 1228)

[3 + 2] cycloaddition (32CA) reactions involving acetonitrile oxide 1 and cis-3,4-dichlorocyclobutene 2 has been investigated via Molecular Electron Density Theory (MEDT) at B3LYP and M06-2X associated with the basis 6–311++G(d,p). The calculated energy profile demonstrates clearly that this reaction is considerably high diastereoselectivity, which is perfectly in accordance with the results of the experiments. The cycloaddition reaction's molecular mechanism has been examined in bonding evolution theory (BET) terms that displays several changes in electron densities along the reaction pathway and demonstrates a one-step process with highly asynchronous transition states. The acetonitrile oxide under study was classified as zwitter-ionic species from the topological analysis of the electron localization function (ELF). In addition, the optimum solvent for performing this cycloaddition is cyclohexane, which is followed by ether and then chloroform. In a further step, a docking survey was carried out for cycloadducts 3, 3-F, 4 and 4-F docked to the main protease of SARS-CoV2 (6LU7) in comparison with ribavirin, revealing that these cycloadducts have lower binding energies than ribavirin.

2023-07

Structural Chemistry (Issue : 4) (Volume : 34)

The mechanism and regioselectivity of [3 + 2] cycloaddition (32CA) reactions of N-methyl-1-phenylmethanimine oxide nitrone 1 and bicyclopropylidene 2 are analyzed using molecular electron density theory (MEDT) at the B3LYP/6–311 + + G(d,p) level. A study of the electron localisation function (ELF) predicts the zwitter-ionic nature of the nitrone, allowing its participation in zw-type 32CA reactions with a high energy barrier that must be surmounted by suitable electrophilic–nucleophilic interactions. The global electronic flux from the strong nucleophilic bicyclopropylidene 2 to the electrophilic nitrone 1 is predicted by an analysis of the CDFT indices. In this 32CA reaction, no new covalent bonds are generated at the TSs, and the mechanism is one-step and kinetically controlled with low asynchronicity in bond formation. The Gibbs free energy of this 32CA reaction in the gas phase is −9.88 and −15.01 kcal.mol−1 for exo and endo path, respectively. The increased thermodynamic stability of the cycloadducts 4 favors the endo regiochemical route. The ELF topological examination at the transition states is in agreement with the predictions of bonding evolution theory (BET) for the endo and exo routes, which point to a one-step process including early transition states.

2023-05

International Journal of Molecular Sciences (Issue : 10) (Volume : 24)

[3+2] cycloaddition reactions play a crucial role in synthesizing complex organic molecules and have significant applications in drug discovery and materials science. In this study, the [3+2] cycloaddition (32CA) reactions of N-methyl-C-4-methyl phenyl-nitrone 1 and 2-propynamide 2, which have not been extensively studied before, were investigated using molecular electron density theory (MEDT) at the B3LYP/6–311++G(d,p) level of theory. According to an electron localization function (ELF) study, N-methyl-C-4-methyl phenyl-nitrone 1 is a zwitterionic species with no pseudoradical or carbenoid centers. Conceptual density functional theory (CDFT) indices were used to predict the global electronic flux from the strong nucleophilic N-methyl-C-4-methyl phenylnitrone 1 to the electrophilic 2-propynamide 2 functions. The 32CA reactions proceeded through two pairs of stereo- and regioisomeric reaction pathways to generate four different products: 3, 4, 5, and 6. The reaction pathways were irreversible owing to their exothermic characters: −136.48, −130.08, −130.99, and −140.81 kJ mol−1, respectively. The enthalpy of the 32CA reaction leading to the formation of cycloadduct 6 was lower compared with the other path owing to a slight increase in its polar character, observed through the global electron density transfer (GEDT) during the transition states and along the reaction path. A bonding evolution theory (BET) analysis showed that these 32CA reactions proceed through the coupling of pseudoradical centers, and the formation of new C-C and C-O covalent bonds did not begin in the transition states.

2023-03

Scientiae Radices (Issue : 1) (Volume : 2)

The zw-type [3+ 2] cycloaddition (32CA) reactions of benzonitrile N-oxide with a series of substituted benzylideneanilines have been studied within the Molecular Electron Density Theory (MEDT) at the B3LYP/6-31G (d) computational level. The presence of dimethylamino and methoxy substituents in the aromatic rings of benzylideneaniline makes the reaction more facile relative to the unsubstituted one, while the electron withdrawing nitro substituents relatively induce minimal changes in the energy profile complying with the experimentally observed reaction rates. The presence of nonbonding electron density at the nitrogen atom and the formation of pseudoradical centre at the carbon atom of benzonitrile N-oxide characterise the difference in electronic structure of the TSs relative to the reagents, while the topological analysis of the electron localization function (ELF) and the atoms-in-molecules (AIM) reveal no covalent bond formation at the early TSs. The present MEDT study analyses the experimentally observed substituent effects and complete regioselectivity in the studied 32CA reactions.

2022-06

Theoretical Chemistry Accounts (Issue : 33) (Volume : 141)

The [3+2] cycloaddition (32CA) reaction of N-methyl-C-(4-hydroxylphenyl) nitrone 1 and maleic anhydride 2 has been investigated using molecular electron density theory (MEDT) at the MPWB95/6-311++G(d,p) computational level. This 32CA reaction undergoes two stereo- and stereoisomeric reaction paths to form two different products 3 and 4. An electron localization function (ELF) study predicts that the N-methyl-C-(4 hydroxylphenyl) nitrone 1 has a zwitterionic character and it takes place through a one-step mechanism, with activation enthalpies in between 17.48 and 23.41 kJ mol−1 in the gas phase. The CDFT indices are used to forecast the global electron density flux from the strong nucleophilic N-methylC-(4-hydroxylphenyl) nitrone 1 to the electrophilic maleic anhydride 2. These exergonic 32CA reactions have negative Gibbs free energy along the endo and exo stereochemical routes. The endo stereochemical process is favored over the exo stereochemical pathway due to the increased thermodynamic stability of the cycloadduct. Bonding evolution theory (BET) predictions for the endo and exo routes indicate a one-step process with early transition states, which is consistent with the ELF topological investigation at the transition states.

2022-01

Structural Chemistry (Volume : 33)

The intramolecular [3+2] cycloaddition (32CA) reactions of azido alkynes leading to spirocyclic, tricyclic, and bicyclic triazolooxazines has been studied within the molecular electron density theory (MEDT) at the MPWB1K/6-311G(d,p) level. The electron localization function (ELF) characterizes the azido alkynes as zwitterionic species. Analysis of the conceptual DFT indices allows classifying the azide moiety as the electrophilic counterpart and the alkyne as the nucleophilic one. These 32CA reactions are under kinetic control with the activation free energies of 23.4–26.7 kcal mol−1. Along the reaction path, the pseudoradical centre is created initially at C4, consistent with the Parr function analysis; however, the sequence of bond formation is controlled by the energetically feasible formation of the six-membered oxazine ring. The intermolecular interactions at the transition states were characterized from the quantum theory of atoms in molecules (QTAIM) study and the non-covalent interaction (NCI) gradient isosurfaces.

2021-12

Journal of the Serbian Chemical Society (Issue : 12) (Volume : 86)

The regioselective synthesis of a potent antiviral sugar nucleoside isoxazole analogue from the 32CA reaction of acetonitrile-N-oxide (ANO) and acetyl-protected 5-ethynyl-2-deoxyuridine (EDU) has been studied at MPWB1K/6-311G (d, p) level within the molecular electron density theory (MEDT) perspective. ANO is classified as a zwitter-ionic species devoid of any pseudoradical or carbenoid centre from the electron localization function (ELF) analysis. The ortho regioisomer is energetically preferred over the meta one by the activation enthalpy of 5.2-5.8 kcal mol-1, suggesting complete regioselectivity in agreeement with the experiment. The activation enthalpy increases from 12.9 kcal mol-1 in gas phase to 17.1 kcal mol-1 in water suggesting more facile reaction in non-polar solvents. The minimal global electron density transfer (GEDT) at the TSs suggest non-polar character and the formation of new covalent bonds has not been started at the located TSs showing non-covalent intermolecular interactions from Atoms-in Molecules (AIM) study and in the Independent Gradient Model (IGM) isosurfaces. The AIM analysis shows more accumulation of electron density at the CC bonding region relative to the CO one, and earlier CC bond formation is predicted from the bonding evolution theory (BET) study.

2021-09

Asian Journal of Applied Chemistry Research (Issue : 3) (Volume : 9)

Theoretical modeling of organic synthesis is a powerful tool and leads to further insight into chemical systems. Computational chemistry allows obtaining the potential energy surface that experimentally cannot be observed, in addition to transition state calculations, which lead to better understanding the reactivity of an organic synthesis work. The Diels-Alder (DA) reaction of cyclopentadiene 1 and N-phenylmaleimide 2 has been studied at the MP2/6-311++G(d,p) level of theory. This DA reaction occurs through a one-step mechanism. It was expected that this reaction undergoes two regio-isomeric reaction paths passing through two different transition states to form two different products 3 and 4. The reaction paths are irreversible due to the exothermic character of -41.24 and -41.73 kcal.mol-1. This DA reaction are exergonic with reactions Gibbs free energies between -27.26 and -27.74 kcal⋅mol−1. Analysis of the CDFT indices predict the global electronic flux from the strong nucleophilic cyclopentadiene 1 to the electrophilic N-phenylmaleimide 2.

2021-08

Zanco Journal of Pure and Applied Sciences (Issue : 4) (Volume : 33)

The Density Functional Theory (DFT) method was used to investigate the stepwise mechanism of the [2+ 2] cycloaddition (22CA) reaction of ketene with methanimine at the B3LYP/6-311++ G (d, p) level of theory. Two modes of attack between reactants were investigated, yielding Azetidin-2-one from path1 and Azetidin-2-one from path2 as two possible products passing through two different transition states. The geometry of transition states and products was analysed. The study of stationary points and energetic parameters shows that the reaction mechanism is stepwise and that Azetidin-2-one P1 is thermodynamically and kinetically more favoured than Azetidin-3-one P2. The analysis of the frontier molecular HOMO and LUMO orbitals shows that the Azetidin-2-one P1 is more stable due to its higher energy gab. The global electronic flux from the strong nucleophilic ketene R1 to the methanimine R2 is predicted using conceptual density functional theory (CDFT) indices. Reactant’s electrophilic and nucleophilic Fukui functions were also investigated.

2021-07

Theoretical Chemistry Accounts (Issue : 7) (Volume : 140)

The [3 + 2] cycloaddition (32CA) reaction of nitronic ester with methyl acrylate has been studied within the molecular electron density theory to analyse the mechanism and experimentally observed regioselectivity. Electron localisation function (ELF) study predicts zwitter-ionic character of the nitrone, allowing its participation in zw-type 32CA reactions associated with high energy barrier demanding overcome through appropriate electrophilic–nucleophilic interactions. Analysis of the CDFT indices predict the global electronic flux from the strong nucleophilic nitrone to the electrophilic methyl acrylate. These 32CA reactions are exergonic with negative reactions Gibbs free energies along ortho regiochemical pathway. Among the ortho and meta regiochemical pathways, ortho path is preferred owing to the higher thermodynamic stability of the cycloadducts. Bonding evolution theory (BET) study predicts one-step mechanism with early transition states for the ortho and meta pathways, in conformity with the ELF topological study at the transition states.

2021-07

Theoretical Chemistry Accounts (Issue : 8) (Volume : 140)

A molecular electron density theory (MEDT) study is performed for the [3 + 2] cycloaddition (32CA) reactions of benzonitrile oxide (BNO) and diphenyldiazomethane (DPDM) to cyclopentene (CP) and norbornene (NBN) with the objective to analyse the experimentally observed acceleration in NBN reactions relative to the CP ones. The activation enthalpy of the 32CA reaction of NBN with BNO is lowered than that of CP by 2.1–2.9 kcal mol−1 in gas phase, DMSO, acetonitrile and THF, while the corresponding differences are 1.3–1.8 kcal mol−1 with DPDM. The 32CA reactions of DPDM show lower activation parameters compared to that of BNO consistent with the respective pseudo(mono)radical and zwitterionic type characters of DPDM and BNO. The syn diastereofacial approach of NBN is energetically feasible compared to the anti one. The global electron density transfer (GEDT) is identified to …

2021-01

Journal of the Mexican Chemical Society (Issue : 1) (Volume : 65)

The [3+2] cycloaddition (32CA) reactions of C-cyclopropyl-N-methylnitrone 1 with styrene 2 have been studied within molecular electron density theory (MEDT) at the B3LYP/6-311++G(d,p) level of theory. These zwitterionic type 32CA reactions occur through a one-step mechanism. The 32CA reactions undergo four stereo- and regioisomeric reaction paths to form four different products, 3, 4, 5 and 6. Analysis of the conceptual density functional theory (CDFT) indices predict the global electronic flux from the strong nucleophilic nitrone 1 to the styrene 2. These 32CA reactions are endergonic with reactions Gibbs free energies between 2.83 and 7.39 kcal.mol-1 in the gas phase. The 32CA reaction leading to the formation of cycloadduct 3 presents the lowest activation enthalpy than the other paths due to a slightly increase in polar character evident from the global electron density transfer (GEDT) at the transition states and along the reaction path. The bonding evolution theory (BET) study suggests that these 32CA reactions occur through the coupling of pseudoradical centers and the formation of new C-C and C-O covalent bonds has not been started in the transition states.

2021-01

Theoretical Chemistry Accounts (Issue : 1) (Volume : 140)

A molecular electron density theory study is presented for [3 + 2] cycloaddition (32CA) reactions of 2,2-dimethyl-1-pyrroline-1-oxide with the nitrile functions to analyse the mechanism and experimentally observed regioselectivity. Electron localisation function (ELF) study predicts zwitter-ionic character of the cyclic nitrone, allowing its participation in zw-type 32CA reactions associated with high energy barrier demanding overcome through appropriate electrophilic–nucleophilic interactions. Analysis of the CDFT indices predict the global electronic flux from the strong nucleophilic nitrone to the electrophilic nitrile functions. These 32CA reactions are endergonic with reactions Gibbs free energies between 5.5 and 39.2 kcal⋅mol−1 in toluene. The ortho regiochemical pathway is preferred owing to the higher thermodynamic stability of the 2,3-dihydro-1,2,4-oxadiazole derivatives. The 32CA reaction of the nitrile function with carbomethoxy substituent is more facile relative to that with the phenyl substituent. Bonding evolution theory study predicts one-step mechanism with early TSs for the ortho pathway, while a one-step-two-stage mechanism is predicted for the meta reaction path, in conformity with the ELF and AIM topological studies at the TSs.

2021-01

Journal of Physical Organic Chemistry (Issue : 2) (Volume : 34)

A molecular electron density theory (MEDT) study for the [3 + 2] cycloaddition (32CA) reaction of indoledione and N‐methyl glycine with (E)‐1‐bromonitrostyrene leading to the spirooxindole‐pyrrolidine adduct is presented. Electron localisation function (ELF) study of the in situ generated azomethine ylide classifies a pseudodiradical electronic structure associated with low activation energies. This 32CA reaction is a polar process with electronic flux from the strongly nucleophilic azomethine ylide to the strongly electrophilic nitrostyrene, confirmed from the global electron density transfer (GEDT) above 0.20 e at the transition states (TSs). Parr function analysis predicts the correct regioselectivity from the two‐centre interactions. The reaction is kinetically controlled with negative free energy of reaction which makes it irreversible. The activation enthalpy of the favoured TS is lowered by 3.4, 6.3 and 9.3 kcal mol−1 in methanol relative to the other feasible reaction paths, consistent with the experimentally observed complete regioselectivity and stereoselectivity. ELF topological characterisation along the reaction path predicts a two‐stage one‐step molecular mechanism, and bond formation is controlled by the nucleophilic character of the azomethine ylide. ELF study, Laplacian of electron density and independent gradient model (IGM) analysis predict non‐covalent interactions at the TSs, where the new C–C bond formation has not been started.

2020-11

New Journal of Chemistry

The [3+2] cycloaddition (32CA) reactions of N-benzylcyclohexylnitrone 1 with methyl-3-butenoate 2 have been studied within molecular electron density theory (MEDT) at the B3LYP/6-311++G(d,p) level of theory. These zwitterionic type 32CA reactions occur through a one-step mechanism. The 32CA reactions undergo two pairs of stereo- and regioisomeric reaction paths to form four different products, 3, 4, 5 and 6. The reaction paths are irreversible due to the exothermic character of −18.5 and −12.4 kcal mol−1. The 32CA reaction leading to the formation of cycloadduct 3 presents the lowest activation enthalpy compared to the other path due to a slight increase in polar character evident from the global electron density transfer (GEDT) at the transition states and along the reaction path. The bonding evolution theory (BET) study suggests that these 32CA reactions occur through the coupling of pseudoradical centers and the formation of new C–C and C–O covalent bonds has not been started in the transition states.

2020-10

Organics (Issue : 1) (Volume : 1)

A Molecular Electron Density Theory (MEDT) study is presented here for [3+2] cycloaddition (32CA) reactions of three trimethylsilyldiazoalkanes with diethyl fumarate. The presence of silicon bonded to the carbon of these silyldiazoalkanes changes its structure and reactivity from a pseudomonoradical to that of a zwitterionic one. A one-step mechanism is predicted for these polar zw-type 32CA reactions with activation enthalpies in CCl4 between 8.0 and 19.7 kcal·mol−1 at the MPWB1K (PCM)/6-311G(d,p) level of theory. The negative reaction Gibbs energies between −3.1 and −13.2 kcal·mole−1 in CCl4 suggests exergonic character, making the reactions irreversible. Analysis of the sequential changes in the bonding pattern along the reaction paths characterizes these zw-type 32CA reactions. The increase in nucleophilic character of the trimethylsilyldiazoalkanes makes these 32CA reactions more polar. Consequently, the activation enthalpies are decreased and the TSs require less energy cost. Non-covalent interactions at the TSs account for the stereoselectivity found in these 32CA reactions involving the bulky trimethylsilyl group.

2020-10

International Journal of Quantum Chemistry (Issue : 3) (Volume : 121)

The [3 + 2] cycloaddition (32CA) reactions of 1‐pyrroline‐1‐oxide with acetylene and with a series of four symmetrically disubstituted acetylenes (XC ≡ CX, X = CH3, NH2, OH, F), leading to 4,5‐disubstituted bicyclic 4‐isoxazolines, have been studied within molecular electron density theory at the B3LYP‐D3/6‐311++G(d,p) computational level. These 32CA reactions take place through a one‐step mechanism, with activation enthalpies in toluene between 24.4 (X = NH2) and 12.9 (X = F) kcal mol−1. Due to the strong exergonic character of these 32CA reactions, between −12.0 and −47.6 kcal mol−1, they are irreversible. The 32CA reaction of difluoroacetylene, involving fluorine as the most electronegative atom of this series attached to the acetylene carbons, presents the lowest activation enthalpy due to the increase of the polar character of this 32CA reaction, evidenced by the analysis of the global electron density transfer at the corresponding transition state structure. The topological analysis of the electron localization function along the reaction paths of these 32CA reactions allows us to characterize them as the zwitterionic‐type ones. The formation of the new C-C and C-O single bonds takes place at the end of the reactions through the coupling of pseudoradical centers.

2020-08

Theoretical Chemistry Accounts volume (Issue : 9) (Volume : 139)

The 1,3-dipolar cycloaddition reaction of benzaldehyde with diazomethane is investigated, in gas phase and in diverse polar solvents, using the molecular electron density theory through density functional theory calculations at the B3LYP(+D3)/6-31G(d) level. Analysis of the reaction pathway reveals that this reaction takes place along a concerted but asynchronous mechanism. Computations show that the acetophenone product is kinetically and thermodynamically more favored than 2-phenylacetaldehyde product in agreement with experimental outcomes. The favored cyclization mode and the observed regioselectivity of this cycloaddition are rationalized by both activation energy calculations, frontier molecular orbital analysis and reactivity indices. Also, polar solvents effect favors the reaction. Furthermore, we performed electron localization function (ELF) topological analysis. The ELF topological analysis of diazomethane indicates that this reactant presents an allenic pseudoradical electronic structure.

2020-05

International Research Journal of Pure and Applied Chemistry (Issue : 7) (Volume : 21)

Pristine and oxygen functionalized multi-walled carbon nanotubes were used as adsorbent for removal of Methyl Orange (MO) dye. The adsorption was carried out under different pH values. The analysis of results indicated that the adsorption characteristics of the MO dye by pristine carbon nanotubes (P-CNTs) and oxygen functionalized carbon nanotubes (O2-CNTs) are highly influenced by the pH of the medium. The study report that the best pH medium of solution for the adsorption of MO on both CNTs was acid medium. The point of zero charge (pzc) of O2-CNTs and P-CNTs were determined as function of pH. The pzc of P-CNTs and O2-CNTs are found to be 4.7 and 3.9, respectively. The adsorption data have been analyzed using Langmuir and Freundlich. Fitting the equilibrium adsorption data by Langmuir and Freundlich models shows that experimental data well explained by the Langmuir equation.

2020-04

Journal of the Mexican Chemical Society (Issue : 2) (Volume : 64)

The reaction mechanisms of [3+ 2] cycloaddition (32CA) between the α, β-unsaturated selenoaldehyde with nitrone and nitrile oxide were investigated theoretically using the molecular electron density theory (MEDT). Selenoaldehyde has two unsaturations which allow for the cycloaddition occurring. It was expected to undergo four regioisomeric reaction paths in two separate reactions with nitrone and nitrile oxide. The study was conducted using ab initio approach at MP2/6-31G (d) level of theory. Potential energy surfaces were generated from the energies of the stationary points involved in the mechanisms and the dominant reaction pathways were identified. It was found that Pathway 3 and 4 are the two competing reaction channels, where the cycloaddition reaction occurs at the selenium-analogue carbonyl group of selenoaldehyde. The reactivity indices were analysed at the ground state of the reactants to predict the reactivity of studied organic molecules in 32CA reactions. Analysis of the electronic structure of nitrone and nitrile oxide, the three-atom-components (TACs), and their participation in 32CA reactions towards selenoaldehyde allows establishing a useful classification of 32CA reactions into zwitterionin-type (zw-type) reactions involving TACs with a high zwitterionic character.

2020-04

International Research Journal of Pure and Applied Chemistry (Issue : 5) (Volume : 21)

The adsorption of Fast Green (FG) dye on pristine multi-walled carbon nanotubes (CNTs) was investigated in this study. The adsorption was carried out under different operating conditions. The operating conditions were contact time, adsorbent dosage, initial dye concentration, the pH of the solution and temperature. The analysis of results found that the removal percentage of FG dye on CNTs decreases with increase in initial FG concentration. It was found that the increasing of CNTs dosage enhanced the efficiency of dye removal. It was also found that the increasing of temperature significantly enhanced the removal percent of FG dye and it is indicated that the adsorption of FG dye on CNTs was in endothermic nature. The study reports that the best pH of solution for the adsorption of FG on CNTs were 4. The adsorption data have been analyzed using Langmuir and Freundlich. Fitting the equilibrium adsorption data by Langmuir and Freundlich models shows that experimental data well explained by the Langmuir equation.

2020-02

Theoretical Chemistry Accounts (Issue : 2) (Volume : 139)

The mechanism of [2+2] cycloaddition reaction of cyclohexenone and its derivatives with vinyl acetate was studied at the B3LYP-D3/6-311++G(d,p) level of theory. Computations showed that this reaction occurs via a stepwise mechanism. The geometries of the first and second transition states were determined. Moreover, we investigated the effect of the chalcogens of the ketone function of the cyclohexenone on the cycloaddition reactions. The activation energies decrease significantly on proceeding from oxygen (O), through sulfur (S) and onto selenium (Se). The energetic results indicate that the stability of the cycloadducts decreases on proceeding from O, through S and onto Se as confirmed by the analysis of their molecular orbitals. Moreover, we determined the pattern of the lowest singlet and triplet electronic states of these species. We proposed an explanation for the regioselectivity of these reactions for the …

2019-12

2019 First International Conference of Intelligent Computing and Engineering (ICOICE)

Diazo dyes compounds have a variety biological and industrial applications. In this study, the molecular structures and the spectroscopic parameters of three synthesized diazo dyes 1–3 were computed using a Density Functional Theory DFT method with the B3LYP/6-311++G(d.p), The results indicate that all three diazo dyes are preferred thermodynamically. Compound 3 has a higher value of entropy and more negative values of heat formation and Gibb's free energy as compared to the other dyes. The FTIR spectra of 2 and 3 show that the nitro functional groups at ortho positions appear at lower symmetrical stretching frequencies. At all, there is a good agreement with the experimental results. On the other hand, the energy gap decreases in this order 2, 3 and 1, also, the FTIR spectrum of compound 1 shows a lower symmetrical stretching frequency of the nitro functional group at the para position.

2019-12

ARO-THE SCIENTIFIC JOURNAL OF KOYA UNIVERSITY (Issue : 2) (Volume : 7)

[4+ 2] cycloaddition reaction has enormous significant in organic chemistry synthesis reactions and yet remains unexplored for the synthesis of fluorine-containing compounds. A density functional theory study of the stereo-and regioselectivity of the [4+ 2] cycloaddition reaction of trifluoroethylene with furan, thiophene, and selenophene was carried out in the gas phase. The B3LYP functional is used throughout in combination with 6-31G (d) basis set. The analysis of stationary points and the energetic parameters indicates that the reaction mechanism is concerted and confirms that the exo-adducts are thermodynamically and kinetically more favored than endo-adducts. The calculated branching ratio indicates that the exo-adducts have the higher percent yield than endoadducts and the yield of endo-adducts is increased only slightly on proceeding from furan, through thiophene, and onto selenophene. The analysis of the frontier molecular highest occupied molecular orbital (MO) and lowest unoccupied MO orbitals indicates that the exo-adducts are more stable due to their higher energy gab. The reaction energies were compared to the MP2/6-31G (d) and CCSD (T)/6-31G (d) calculations.

2019-10

Oriental Journal of Chemistry (Issue : 5) (Volume : 35)

This study presents the intramolecular [2+ 2] cycloaddition reaction of ketenes to form cyclobutanones using B3LYP-D3/6-311++ G (d, p) level of approximation. The concerted mechanism path was studied in detail. The structures of all intermediates and transition states were located using same level of theory. The influences of the substituents (-H,-CH3,-NH2,-F,-OH and–CN) were also discussed. The analysis of stationary points and the energetic parameters indicates that the substituted ketene with–CN group has the highest activation energy; however, ketene with–NH2 group has the lowest one. Conversely, in-tramolecular [2+ 2] cycloaddition records the highest degree of asynchronicity with–NH2 group and lowest with–CN group. The calculated thermodynamic parameters at room temperature have been listed and analyzed. The global and local properties of reactants involved in the intramolecular [2+ 2] cycloaddition reactions and the Fukui functions for an electrophilicity and local electrophilicity were also elucidated for carbon centers of each reactant.

2019-06

Science Journal of University of Zakho (Issue : 2) (Volume : 7)

This work investigates the electro-catalytic degradation of alizarinblack dye in an electrochemical cell using Fe as anode and Al as cathode. The influence of initial dye concentration, effect of salt, pH, change of temperature and effect ofchange of applied voltage have been studied in addition, the influence of semiconductor dose has studied as well. In the current work roughly total removal of 70 mg/L of dye occurred in 16 minonly. The results showedthat effect of both electrolyte concentration and applied voltage was positive if combined together and the rate of degradation in neutralmedium was the best for degradation of Alizarin black dye.

2018-12

IOP Conference Series Materials Science and Engineering (Issue : 1) (Volume : 454)

A theoretical study of the photochemical dimerization of allyl 3-(2-pyridyl) acrylate and allyl 3-(2-pyrryl) acrylate is reported. The reactions gave dimers with high regioselectivity and stereoselectivity through [2+2] cycloaddition mechanism. All calculations were computed by density functional theory method, B3LYP, in conjunction with the 6-31G(d) basis set. Conformation analysis, geometric parameters and IR spectrum for the target dimers were also studied. Conformation 2 of allyl 3-(2-pyridyl) acrylate and conformation 9 for allyl 3-(2-pyrryl) acrylate were found to be the most stable structures among the different conformations. Vibration frequencies and IR absorption intensities were calculated for the conformers 2 and 9 using the same computational method. In addition, thermodynamic parameters for the reactions of most stable conformations were analysed. The HOMO and LUMO molecular orbitals and the energy gap between them were estimated for the stable conformations.

2018-11

2018 International Conference on Advanced Science and Engineering (ICOASE)

The photo-catalytic degradation of Toluidine Blue dye (TB) in aqueous suspension solution has been studied utilizing fluorescence light and using Zinc oxide (ZnO) as a semiconductor at variety working factors. The studied parameters were concentration of dye, semiconductor dose and the influence of pH. The result shows that expanding of ZnO dose from 20 to 60 mg/L increases the removal rate of TB dye. On the other hand, the adding of concentration from 5 to 15 mg/L show negative effect on the rate of photo-degradation. It has been denoted that the percentage of dye degradation come to the peak value at high acidic medium. 11 % of TB dye was adsorbed, in dark condition, by ZnO. In addition, the kinetics of degradation has been examined and the degradation was found to take after pseudo-first order kinetic model.

2018-11

2018 International Conference on Advanced Science and Engineering (ICOASE)

The Paterno-Büchi reaction of benzene with benzaldehyde and furan with furfural were studied theoretically. The mechanism was investigated using Density Functional Theory (DFT). It was found that the final product of the benzene reaction is oxetane 3, while in the case of furan the oxetane 6 is unstable and goes through oxetane ring opening. The target of this article was to study the reaction mechanism and calculate the thermodynamic parameters of the reactions. The oxetane 3 formed was found to be stable with reaction energy of -120 kcal/mol. However, the oxetane 6 was found to be less stable with reaction energy 21 kcal/mol which tends to produce more stable product 7 through the oxetane ring opening. In addition, the molecular orbitals were calculated and analyzed for all the intermediates, oxetanes and final products.

2017-09

Science Journal of University of Zakho (Issue : 3) (Volume : 5)

Pollution of wastewater with heavy metal has always been a serious problem to the environment. Chromium is considered one of the most noxious heavy metals. Adsorption is now reorganized as an alternative technology of defence for chromium removal due to local availability, technical efficiency and cost effectiveness. Potato peel powder can be used as a low cost biosorbent to remove hexavalent chromium from aqueous solutions under various experimental conditions. Different parameters including equilibrium contact time, initial metal ion concentration, potato peel dose, pH and temperature were studied through a number of batch sorption experiments. Both the Langmuir and Freundlich were found to fit the adsorption isotherm of Cr (VI) ion onto potato peel. The Langmuir adsorption capacity was found to be 1.97 mg/g while Freundlich constants including Kf and n were 1.57 and 2.5, respectively. The adsorption kinetic was found to be more fit with the pseudo-first order model. This study showed a high efficiency of potato peel for the biosorption of Cr (VI) ion from aqueous solutions.

2017-06

Science Journal of University of Zakho (Issue : 2) (Volume : 5)

This study was carried out to examine the concentrations of major heavy metals in fifteen different well water in Zakho City, Kurdistan Region, Iraq. The studied heavy metals were iron, copper, chromium, aluminum, cadmium, cobalt, nickel, manganese, zinc and lead. The results obtained in the studied area showed that copper, chromium, cobalt, zinc, manganese, aluminum, iron and lead were within the acceptable limits as recommended by WHO for water drinking. However, in all studied areas, cadmium and nickel were mostly founded to exceed the maximum permissible limit set by WHO. It is found that zinc and copper possess a very good positive correlation between each other. The results obtained in this study confirmed the groundwater pollution and hence it is not suitable for consumption without any prior treatment.

2016-04

2nd INTERNATIONAL SCIENTIFIC CONFERENCE – UNIVERSITY OF ZAKHO (Volume : 2)

The degradation of commercial textile dye named fast green (FG) was investigated by Fenton reagent under different operating conditions in an aqueous solution. The operating conditions were amount of hydrogen peroxide (0.05, 0.1 and 0.15 mL), pH (2-12) and concentration of ferrous ion (10, 20 and 30 mg). The initial rate of degradation was affected by the concentration of Fenton reagents [Fe(II) and H2O2 solution]. The rate of degradation enhanced as the concentration of ferrous ion increased. As the ferrous ion concentration increased from 10 to 30 mg, the removal percent was increased from 73% to 89%, respectively, at 25 min of reaction time. Also, the removal percent of FG increased from 74 % to 81 % as the amount of H2O2 increased from 0.05 to 0.15 mL, respectively, at 25 min of reaction time. it was also found that at pH 3 removal percent reach maximum value with 91.8%. The kinetic study of FG degradation was also studied in this work and the results indicated that the degradation kinetics of FG followed the first-order kinetic.

2016-03

international Research Journal of Pure & Applied Chemistry (Issue : 2) (Volume : 11)

The adsorption of Acid Alizarin Black (AAB) dye (C.I. 21725) on zinc oxide was investigated in this study. The adsorption was carried out under different operating conditions. The operating conditions were contact time, adsorbent dosage (10, 30, 50, 70 and 100 mg), initial dye concentration (10, 20, 30, 40, 50, 60 and 70 mg/L), the pH of the solution (2, 4, 6, 7, 8, 10 and 12) and temperature (20, 30, 40, 50 and 60°C). The removal percentage of dye on ZnO decreases from 67% to 54% with increase in initial dye concentration from 10 to 70 mg/L, respectively. It was found that the increasing of ZnO dosage enhanced the dye removal. The increasing of temperature insignificantly enhanced the removal of dye. The study reports that the best pH of solution for the adsorption of AAB on ZnO were 7 and 8. The adsorption data have been analysed using Langmuir, Freundlich and Temkin. It is indicated that the adsorption of dye onto ZnO was endothermic. The uptake process of AAB obeyed the pseudo second order kinetic expression. Removal of Acid Alizarin Black Dye from Aqueous Solution by Adsorption Using Zinc Oxide.

2015-09

International Journal of Chemistry (Issue : 2) (Volume : 7)

The photocatalytic degradation of Toluidine Blue dye (TB) in aqueous solution was investigated under UV light in the presence of magnesium oxide (MgO) as a photocatalyst at different operating parameters. The operating conditions were photocatalyst dose, initial dye concentration and the pH of the solution. Increasing of photocatalyst dose from 10 to 70 mg enhanced the degradation rate of TB dye. However, the increasing of TB dye concentration from 2 to 8 mg/L negatively affected the degradation rate. It was found that the percent of dye removal reached the maximum value at high acidic medium. In dark condition, 15 % of dye was adsorbed by MgO. Furthermore, the kinetics involved in the degradation of TB dye was examined and the degradation was found to follow pseudo first order kinetic model.

2015-08

Journal of Environmental Engineering and Science (Issue : 8) (Volume : 4)

Zinc oxide (ZnO) has been used as heterogeneous catalyst for the degradation of Acid Alizarin Black S dye (AAB) in aqueous solutions using UV light irradiation. Experiments were conducted at various operating parameters. The operating parameters were amount of catalyst (50 mg, 100 mg and 150 mg), initial concentration of dye (30 mg/L, 50 mg/L and 70 mg/L), the pH of solution (2, 4, 6, 8, 10 and 12) and the UV light intensity (6 watt and 12 watt). The progress of the degradation reaction was monitored spectrophotometrically. It was found that the degradation process of AAB solution was accelerated with increased catalyst dosage and decreased initial concentration of AAB. It was also found that the removal efficiency of AAB significantly depend on pH value of solution. The results show that the degradation percent reaches the highest values with pH close to neutral. The data proved that removal percent of dye decreased when 6 watt lamp used instead of 12 watt lamp. The kinetic study confirmed that photocatalytic degradation of AAB dye follows a pseudo first order reaction rate.

2015-02

International Journal of Advanced and Applied Sciences (Issue : 2) (Volume : 2)

Acid alizarin black (AAB) dye (C.I. 21725) was degraded in aqueous solution using UV light in the presence of two types of clay (C1 and C2) as a catalyst at different operating conditions. The operating conditions were concentration of catalyst dosage (10, 30 and 50 mg), initial concentration of AAB dye (10, 20 and 30 mg/L), pH (2, 4, 6, 9 and 11) and intensity of UV light (6 and 12 watt). It was found that the increasing of catalyst concentration enhanced the dye decolourisation. C1 and C2 exerted positive effects on the AAB removal whilst the initial concentration of AAB negatively affected its removal. It was also found that the removal efficiency of AAB significantly depend on pH value. In high and low pH values removal percent increase, while a reversed trend was observed at with the pH value close to neutral. The result shown that removal percent of dye increased when 12 watt lamp used instead 6 watt lamp. C1 and C2 clay were analysed by X-Ray fluorescence to determine the metal oxides in clays.

2014-10

Ozone: Science & Engineering: The Journal of the International Ozone Association (Issue : 3) (Volume : 37)

Multiwalled carbon nanotubes functionalized by plasma oxygen (CNTs) have been used as heterogeneous catalysts for the ozonation of methyl orange (MO) dye (CI 13025) in aqueous solutions. It was found that the addition of CNTs significantly enhanced the dye decolorization as compared to ozone alone or when activated carbon was used at the same dose as CNTs. Both the initial ozone concentration and catalyst dosage enhanced the removal of MO. However, ozone gas concentrations higher than 6 g/m3 NTP did not further improve the decolorization rates. The removal efficiency of MO increased with pH in the range 2 to 3, while a reverse trend was observed when the pH increased from 3 to 9. The addition of a radical scavenger resulted in only a limited change in the decolorization rates suggesting that molecular ozone was the main pathway by which MO decolorization occurred in solution. However, under favorable conditions for MO attraction to CNT surface (pH = 3), the decolorization rate has significantly increased. At higher pH than the pKa value of MO (3.47) and the point of zero charge of CNT (3.87), a condition that favors the electrostatic repulsion of MO from CNT, the rates were reduced in the presence of CNT as compared to ozone alone possibly due to loss of part of the supplied ozone in un-useful parallel reactions

2014-10

Journal of University of Zakho (Issue : 2) (Volume : 2)

Photocatalytic degradation of acid alizarin black (AAB) dye (C.I. 21725) in aqueous solution was investigated using UV light in the presence of hydrogen peroxide (H2O2) as a catalyst at different operating conditions. The operating conditions were concentration of catalyst dosage (0.1, 0.2 and 0.3 mL of 30 % H2O2), initial concentration of AAB dye (100, 150 and 200 mg/L) and pH (3.3, 6.84 and 10.8). It was found that the increasing of catalyst concentration enhanced the dye decolourisation. Hydrogen peroxide exerted positive effects on the AAB removal whilst the initial concentration of AAB negatively affected its removal. It was also found that the removal efficiency of AAB increased with the pH value close to neutral (pH 7), while a reversed trend was observed at acidic and basic medium.

2014-06

Journal of University of Zakho (Issue : 2) (Volume : 2)

Photocatalytic degradation of acid alizarin black (AAB) dye (C.I. 21725) in aqueous solution was investigated using UV light in the presence of powder of titanium dioxide (P- TiO2) and nanoparticles of titanium dioxide (N- TiO2) as a catalyst. The operating conditions were catalyst dosage (10 and 20 mg/L) and initial concentration of AAB dye (10 and 20 mg/L). It was found that the increasing of catalyst concentration enhanced the dye decolourisation. Both catalysts exerted positive effects on the AAB removal whilst the initial concentration of AAB negatively affected its removal.